This invention relates to a lamp apparatus for use in optical communication, more particularly to a lamp apparatus for use in optical communication that has a trough-shaped parabolic mirror. The invention relates specifically to a lamp apparatus for emitting light to receivers for optical communication that are arranged in a line. Stated more specifically, the invention relates to a small lamp apparatus that permits IR carried data to be transmitted in the space through angles of .+-.60 degrees on the horizontal 4 m ahead, namely, in a line about 7 m long to either right or left.
FIG. 11 shows the layout of conventional systems of indoor local area network (LAN), a language laboratory (LL) learning facility, an amusement facility such as pin-ball machines (pachinko in Japanese) and cash registers in a department store. Individual machines 111-114 arranged in a line several meters long on both the right and left sides communicate data with a controller 110 via dedicated cables 121 and 122. A problem with this system is that if the machines 111-114 are changed in position or if additional machines 115-117 are installed, cabling work must also be done in the ceiling 131, walls 132 and on the floor 133, requiring much cost and time. In addition, performing a complex cabling operation on more than one machine has been a labor-intensive job.
If IR light is used as a carrier, data can be transmitted through the space without using the dedicated cables 121 and 122. Data communication using an IR light-emitting diode (LED) has heretofore been used in limited applications but due to the structural constraints of the leadframe in the LED, the current that can be applied is limited and in order to achieve consistent data transmission over a long distance, many IR lamps are necessary, resulting in an increased cost. As will be apparent from FIG. 13, the current that can be applied is limited simply because the leadframe 811 of the LED 411 which is a component of the lamp 511 has a very small cross-sectional area; in other words, the heat channels available are so narrow that the heat generated by the LED 411 in operation cannot be dissipated to the ambient very rapidly.
A further problem with the prior art is that no lamp has been available that can distribute IR light over a broad range in both right and left directions. To overcome this difficulty, several LED lamps are combined to fabricate a desired lamp assembly as shown in FIG. 14. However, the lamp assembly 611 takes much time to construct since a plurality of individual lamps 511 have to be assembled and, what is more, the fabricated lamp assembly 611 is too bulky to be used in a limited space. In addition, as shown in FIG. 15, the combination of lamps 511 provides a luminous intensity distribution pattern 711 that covers a wide range in a horizontal direction but, at the same time, unwanted light is emitted in a vertical direction, simply resulting in a waste of electric power.
Stated briefly, the combination of IR lamps has already been proposed in order to provide a luminous intensity distribution pattern that covers over a broad range in a horizontal dIRection and which is far reaching; however, assembling a plurality of IR lamps is time-consuming and, in addition, the light issuing in a vertical direction is simply a waste of energy.